It is important that various industrial structural members such as aircraft and other vehicle interior parts, upholstery materials and building materials be as light in weight as possible and yet retain sufficient rigidity and strength. For this reason, rather than shaping such structural member in flat or curved plate form it has been common practice to shape it as a cubic structure having a plurality of planar structural sections made continuous by crossing each other, a cubic structure, for example, in substantially T, Y, I or H form in cross-section, that is, a three-dimensional structure.
Conventionally, structural members formed of plastic forms reinforced by fiber, or so-called fiberglass reinforced plastics (FRP) have been widely utilized. However, where such structural member is formed as a three-dimensional structure having a plurality of planar structural sections, as described above, there is a problem concerning strength and durability particularly in joined portions where planar structural sections are joined together. Further, such structural member tends to produce warp or strain and when loaded it is liable to produce buckling, deformation or peeling, thus failing to provide sufficient strength.
Particularly concerning a structural member used as an aircraft or other vehicle interior part, there has been a desire for such member which is of said cubic construction resistant to bending and which is light in weight in use and can withstand continuous vibration or shock. However, said structural members formed solely of plastic material cannot meet such requirements.
For this reason, in recent years, trials have been made using a textile fabric as a reinforcing core material, impregnating it with synthetic resin, followed by molding and solidification, and then forming it into a three-dimensional cubic structural member having a substantially T-shaped or I-shaped cross-section, and various proposals have been made concerning reinforcing core materials for use therewith.
For example, Japanese Patent Application Laid-Open No. 176232/1982 discloses a technique wherein fiber groups of first direction forming warp yarn layers and fiber groups of second direction forming weft yarn layers are alternately piled in large numbers without being woven so as to form a laminar structure, said wrap and weft yarn layers being bound together to present a laminar form bisected at opposite lateral ends in the direction of the length by a third group of fibers to thereby form a fabric, said fabric being used as a reinforcing core material, which is then impregnated with resin and molded, whereupon the bifurcations are opened and the structure is solidified, thereby forming an H-shaped structure. With this technique, there is obtained a structural member having thick planar structural sections; however, since the warp and weft yarn layers are not interlaced, the two yarn layers are relatively weakly bound and particularly in the lateral edges of the fabric the widthwise arrayed weft yarn are in the broken state, resulting in the danger of the warp yarns being frayed before resin impregnation and solidification are completed, their adherence to the resin with which they are impregnated being low; thus, it is impossible to obtain sufficient mechanical strengths such as vibration resistance and shock resistance.
Further, as disclosed in Japanese Patent Application Laid-Open No. 133241/1982, there is a structure wherein in a fabric formed of warp and weft yarns crossing each other, one or both ends in the direction of the width are woven into a double fabric. However, this technique is based simply on the crossing of yarns in two directions, warp and weft, and since the weft yarns arrayed widthwise in the lateral ends of the fabric are broken, there is the danger of the warp yarns in the lateral ends being frayed during handling before resin impregnation and solidification are completed, resulting in a lack of integrality with the solidified resin; therefore, it is impossible to obtain sufficient mechanical strengths such as vibration resistance and shock resistance.